Micropollutants such as pharmaceutical residues and other emerging substances are removed from wastewater to a very limited degree by existing treatment processes. The micropollutants typically pass through modern sewage treatment plants (STPs) and end up in receiving waters and sludge. Several studies have detected micropollutant concentrations in receiving waters and sludge at levels detrimental to aquatic organisms.
The term “micropollutants” relates to organic or mineral substances whose toxic, persistent and bioaccumulative properties may have a negative effect on the environment and/or organisms (e.g. the feminisation of fish due to endoctrine-effect substances in the aquatic environment), and even on human health. Micropollutants are trace compounds that occur in small amounts in the environment. They are present in many products that we consume daily (drugs, cosmetics, phytosanitary products, insecticides, etc.), at the home or in industry.
There are many different classes of micropollutants. Among them are pharmaceuticals, such as contraceptives, painkillers, lipid regulators, beta-blockers, antibiotics, tranquilizers, and psychostimulants. Over 200,000 different drugs and health products are registered in the US, Canada, European Union, Japan, and other countries. In wastewater and surface water, human and veterinary pharmaceuticals typically occur in low range concentrations of ng/L (e.g. synthetic hormones), low to high range concentrations of ng/L (e.g. ß-blockers, antibiotics and antiepileptics), and up to concentrations of hundreds of ng/L (e.g. painkillers, lipid regulators and X-ray contrast media). However, there are also many other classes, such as personal care products (PCPs), biocides, and industrial chemicals. Apart from man-made micropollutants, minute quantities of naturally-occurring toxicants, such as mycotoxins (e.g. nicotine), mycotoxins, and pyrethrins, are present and can affect organisms.
Current sewage treatment plant treatment technologies are usually not able to remove micropollutants. Physical tertiary treatment of micropollutant-containing wastewater using adsorption materials such as activated carbon filtration to remove micropollutants is known in the art. However, while activated carbon is able to remove soluble micropollutants from wastewater, separation and disposal of the micropollutants from the carbon is then required. Advanced oxidation with oxidising agents such as ozone is expensive and oxidation of the micropollutants may lead to new compounds that are potentially more toxic and require further treatment before disposal.
Microbial degradation of micropollutants has been suggested as an energy efficient solution to solve the draw-backs with ozonation and activated carbon.
Microbial degradation of micropollutants with technologies that typically provide long sludge retention times, such as membrane biological reactors and moving bed biofilm reactors (MBBRs), have shown promise at removing micropollutants. However, implementing tertiary treatment for micropollutant removal with a biological system has been limited by factors including sustaining the amount of microbial biomass available for the degradation and the low concentration of micropollutants in the wastewater. In turn this has led to low micropollutant removal rates.
WO 00/15565 A2 discloses a bioreactor having a bed of buoyant media pellets floating within a filtrate to be processed. The bioreactor is used to culture microorganisms and algae for various purposes.
EP 1 431 252 A2 discloses a filter element for a clarification device for biological water treatment. The filter has a biological treatment stage in which water is treated by aerobic microorganisms resident on a shallow, dished body that is open on one or both sides.
CN 201896101 U discloses a microbe suspending medium for a moving bed biofilm reactor that enlarges the carrier surface area, is beneficial for adhering and growing microbes, and increases the contact rate of a biofilm and oxygen.
WO 2013/151836 A1 discloses a process for removing ammonium from a wastewater stream. The process utilises ammonium oxidizing bacteria (AOB) and anaerobic ammonium oxidizing bacteria (ANAMMOX).
Pusker Regmi et al.: NOB Repression for Mainstream Nitrite-Shunt and Deammonification: A Pilot Study. WEFTEC 2013. Proceedings of the Water Environment Federation, WEFTEC 2013: Session 26 through Session 34, pp. 1959-1981 (23) disclose a two stage study to prove the viability of mainstream NOB suppression and deammonification in wastewater treatment.
There remains a need for an improved method of treating wastewater to remove micropollutants therefrom.